1. Field of the Invention
The present invention generally relates to the general field of protecting integrated circuits against unwanted intrusion or tampering. More particularly, this invention relates to a sensor circuit and a method, which uses metal wire loops to protect integrated circuit dies from unwanted tampering.
2. Description of the Prior Art
The circuitry and memory of certain integrated circuits are sensitive and need to be protected from unwanted tampering. Various applications such as automatic teller machines, ATMs, require a high level of protection from external tampering and deciphering of the circuitry and memory. Similarly, pay-per-view television cable boxes require protection against intruders who may attempt to steal cable services by tampering with circuits and memory within the cable boxes. Previous means of protecting circuits include passivation layers covering the sensitive electronic layers. Security boxes also have been used to enclose the sensitive circuitry. Electronic techniques include imbedding security microprocessor macros on the same chip as the circuitry to be protected. These security processor macros have the means of generating random keys and other cryptographic data objects which are used to render the contents of memory such as electrically erasable programmable read only memory (EEPROM) unreadable even if the data is successfully obtained.                U.S. Pat. No. 5,533,123 (Force et al.) describes a Secured Processing Unit (SPU) chip, a microprocessor designed especially for secure data processing. The system is based on 3 interrelated systems: 1) detectors to alert the SPU of an attack, 2) filters to weigh the severity of the attack, 3) responses or countermeasures to deal with the attacks. The system provides much flexibility via programming the SPU.        U.S. Pat. No. 5,881,155 (Rigal) describes a security device for preventing access to confidential information stored in a semiconductor chip, or protected chip. The security device comprises a second semiconductor chip, or protective chip, with the two chips facing each other and being coupled to each other by communication terminals. The protective chip can measure resistances through the semiconductor resin and can determine, at least from the measured resistances, an encryption key intended to be communicated to the protect chip to protect the confidential information.        U.S. Pat. No. 6,245,992 (Hou) describes a an integrated circuit (IC) chip security box which includes a top cover member and a bottom cover member to enclose an IC chip mounted to the circuit board. The cover members are made of conductive material for blocking radio frequency emission from the IC chip. Conductive members are formed on one of the cover members and the circuit board and engage with each other when the security box is mounted to the circuit board thereby forming an electrical loop. Unauthorized opening of the security box breaks the electrical loop thereby causing a signal to the IC chip to initiate a purging process which deletes program codes written in the chip and prevents unauthorized copy of the codes.        
However, the various prior art protection schemes mentioned are either very complex or they require a substantial about of power dissipation within the integrated circuit.